The present invention relates to a method for producing paper feed rollers in which a hydraulic composition is used for roller portions and which are employed in apparatuses, such as printers, facsimile machines and copying machines, requiring papers to be accurately conveyed.
Formerly, metallic rollers, rubber rollers, etc. have been used as paper feed rollers. The metallic rollers have been each produced by attaching end plates with shaft portions to both end portions of a hollow metallic cylindrical body constituting a roller portion, respectively, by welding. In this case, although a rotary shaft of the metallic roller is formed by the shaft portions at the opposite ends, there is a very difficult problem in ensuring the concentricity between the metallic cylindrical body and the rotary shaft. Further, paper feed rollers in which a roller portion is constituted with hard rubber to reduce the weight have been used, but there is a problem in that errors are likely to occur in feeding papers owing to large heat expansion of the roller portion.
In order to solve the above-mentioned problems, Sumitomo Osaka Cement Co., Ltd. made an invention directed to a method for the production of an integrated paper feed roller by preparing a cylindrical molded body having a given length from a hydraulic composition according to a press molding method and fixing the molded body around the outer periphery of a rotary shaft, and Sumitomo Osaka Cement Co., Ltd. filed an application therefor under Japanese Patent Application No. 10-177,100. Further, Sumitomo Osaka Cement Co., Ltd. filed patent application under Japanese patent application No. 11-28,137, etc. directed to a method for the production of paper feed rollers in which roller portions are formed by connecting a plurality of cylindrical molded bodies.
According to this method, since the length of the cylindrical molded bodies themselves can be shortened as compared with that of a desired roller portion, non-uniform pressure applied during the press molding can be prevented, and a shaping mold can be made smaller. Further, if the length of a single cylindrical body is set based on the relationship between the size of papers and the number of such cylindrical molded bodies to be connected, and a plurality of the cylindrical molded bodies having a single shape are preliminarily prepared, plural kinds of paper feed rollers can be easily produced depending upon the sizes of papers by using given numbers of the cylindrical molded bodies having a single shape. This enables the inexpensive mass production of the paper feed rollers with a high precision.
However, since the roller portion is formed by connecting plural cylindrical molded bodies in the above method, there is a problem in that the hardness of the roller portion is low. Further, although the rigidity can be increased by appropriately selecting an adhesive used in the connecting portion, it leads to cost-up, and there is a limit for the increase in the rigidity.
The present invention is aimed at solving the above problems, and providing a paper feed roller-producing method capable of mass-producing, with a higher precision at a more inexpensive cost, a high-precision paper feed roller having no connecting portion at a roller portion according to an extrusion molding with use of a hydraulic composition.
The paper feed roller-producing method according to the present invention is a method for producing a paper feed roller comprising a rotary shaft and a cylindrical roller portion integrated around the outer periphery of the rotary shaft, characterized in that the roller portion is formed by extruding a hydraulic composition and curing and hardening the extrudate product.
The following will be recited as preferred embodiments of the paper feed roller-producing method according to the present invention.
(1) A hollow cylindrical molded body is extruded from the hydraulic composition, the rotary shaft is inserted through a hole of the molded body, and the molded body is cured and hardened to integrate the rotary shaft and the roller portion.
(2) A hollow cylindrical molded body is extruded from the hydraulic composition, the molded body is cured and hardened, and the rotary shaft is inserted through a hole of the molded body to integrate the rotary shaft and the roller portion.
(3) A hydraulic composition is concentrically extruded around the rotary shaft, and cured and hardened to integrate the rotary shaft and the roller portion.
Among the above, the method (3) is most preferable.
The hydraulic composition preferably comprises 100 wt. parts of a mixed powder, 2 to 9 wt. parts of a workability improver, and 0.5 to 5 wt. parts of a thickening agent, said mixed powder comprising 40 to 80 wt % of a hydraulic powder, 10 to 50 wt % of a non-hydraulic powder having the average particle diameter smaller than that of the hydraulic powder by an order of one digit or more, and 10 to 30 wt % of an extrusion improver
The extrusion improver is preferably an inorganic scaly material. As the inorganic scaly material, talc and mica may be recited.
The workability improver is preferably a powder or emulsion composed of at least one resin selected from a vinyl acetate resin or a copolymer resin with vinyl acetate, an acrylic resin or an acrylic copolymer resin, a styrene resin or a copolymer resin with styrene and an epoxy resin